The Charter's minimal language has since been supplemented by other procedural rules and accepted practices. In practice, the Secretary-General cannot be a national of any of the permanent members of the Security Council. An accepted practice of regional rotation has also been adopted in the selection of successive candidates. The ability of candidates to converse in both English and French is also considered an unofficial qualification for the office.

When the race to succeed Annan began in 2006, it was widely expected the successful candidate would be Asian, since a number of Security Council members (including China, which has a veto) indicated they would only support an Asian candidate.[2]

The Security Council conducted four straw polls, on 24 July,[9] 14 September,[10] 28 September,[11] and 2 October,[12] in which each of the 15 member states were asked whether they would "encourage" or "discourage" each of the official candidates (or if they had ‘no opinion’ on the candidate). Ban Ki-moon and Shashi Tharoor topped each of these polls. In the fourth poll, Ban emerged as the only candidate with the support of all five permanent members, each of whom has the power to veto candidates; Shashi Tharoor had received more overall "encourage" votes in some previous straw polls but China indicated it would veto Tharoor, who is Indian. One Permanent Member (later revealed to be the US under the Bush Administration)[13] opposed and China abstained from voting. After the vote, Shashi Tharoor, who finished second, withdrew his candidacy[14] and China's Permanent Representative to the UN told reporters that "it is quite clear from today's straw poll that Minister Ban Ki-moon is the candidate that the Security Council will recommend to the General Assembly".[15]

Zeid and Ghani withdrew from the race on 4 October.[16] They were followed on 5 October by Surakiart and Vīķe-Freiberga, leaving only Ban in the race.[17] The Security Council conducted a formal vote on 9 October, and forwarded its choice to the General Assembly, which then elected him on 13 October.[18]